Leon was never a model citizen. Even before his jump to a post-apocalyptic world, he was arrogant, cynical and irritable. And his fifteen years there have done nothing to improve his attitude, except leave him at least partially insane. He doesn't have much respect for anyone outside of his friends and doesn't really care who he mouths off to if his friends tell him to put a sock in it first.
However, he is very good at what he does. He first learned how to be an engineer/mechanic by repairing himself and his sixlets in a post-war world where resources were sparse. In addition, as an electrical engineering robot, he had a natural gift for the field to begin with (thanks to in part schematics that were previously uploaded to Elecman's memory banks). And now that he's back in a world with more plentiful resources, his ingenuity is his only limit. In combat, he's good at thinking on his feet and making the most of his gifts to come out on top each and every time. Even though he buys his own hype, he's still a reliable ally who'll always drop everything to help his friends if they're in trouble.
Outside of his crafts, he's nothing if not incompetent. Mostly because he doesn't have the patience for long-term thinking. But since he's good at thinking on the fly, he gets out of his fixes as easily as he gets in them. And he still cares deeply about his teammates. Even if he chooses to show it in a smarmy way.
Differences between Spark and DiveEdit
It's been pointed out that the difference between Leon and Dive is fairly murky at times. And I'd be lying if I said that wasn't true. But there are a few differences between the two of them.
For starters, Leon's not nearly as drunk or belligerent as Diveman is. And Leon's generally much more articulate (in the sense that he speaks using real words). Diveman's a thug looking for an excuse to beat someone up and just be a dick. Leon's a hotshot goofball who believes his own hype (some of which could be self-imagined). While they're both just as likely to piss off the wrong person by being a smartass or a jerk, Leon's smart enough to know when to back down and talk his way out. Diveman...not so much. Just ask Hardman. Leon's not nearly as lucky as Diveman is. He's more likely to get into some awkward situations than Dive is, because Dive is a jerkass Mary Sue who thinks God is on his side (and actually, she is). And as Sparkman, Leon's more technically minded than Dive is.
But there you have it. They're both jerkasses. But different shades of jerkass.
As Elecman Leon wore the Transmetal version of that armour, which generally was just a more powerful version of the base Elecman. As Sparkman Leon wore a version of the Transmetal 3 armour, modified to fit his frame and personal abilities. After returning his Elecman armour was so heavily damaged that it is no longer usable.
After being kidnapped and modified by General Cutman during the War Leon's natural talent for engineering was enhanced and he became an expert mechanic. One of his greatest feats was building a portal back to the Epiverse (based on one left behind in the OH universe).
After Gary's passing, the grief-stricken Leon was easily swayed/manipulated by General Cutman into serving in the SA, on the pretences of having a family again. Eventually, the Maniacs overcame him and the rest of his SA-ized allies, and brought them back to their normal selves. When the Gary from General Cutman's world entered ours, Leon and the remainder of the S6 jumped at the opportunity to be a family again and accompanied him back to his world, where they continued to have adventures and sweep up the SA in a ruined world torn apart by genocide and war.
Fifteen years later, Leon returned to this world to help gather some supplies to rebuild his world, only to be stunned that the Mechs are no longer perceived as the heroes they once were. And to make matters worse, some surviving SA officers followed him through the portal, intent on invading a new world. Even though they were forced back, it left Leon stranded in this world. The Mechs needed a new Sparkman, Leon needed a new armour, and since Leon couldn't move the resources he needed or even rebuild the portal without restoring the Mechs' good name, they decided to help each other out.